A morganatic marriage is often only contracted by royalty and non-royal individuals. Morganatic marriage was originally a German custom and a way to handle an unconventional union.
German term is unebenbürtig or ehe zur linken hand. The source of the term is from the German morgengabe which means "morning gift." Morning gift refers to an old custom of the husband presenting his wife with a gift the morning after their marriage was consummated. In a morganatic marriage, that was the only gift she would receive.
From the Latin phrase matrimonium ad morganaticam.
Morganatic Marriages in HistoryArchduke Franz Ferdinand and Sophie Chotek von Chotkowa
Prince Alexander of Hesse and Countess Julia von Hauke
Prince Alexander of Württemberg and Claudine Rhedey
Ludwig Wilhelm, Duke in Bavaria and Henriette Mendel
Louis XIV of France and Madame de Maintenon via a secret marriage